Week 1: Evidence of Chemical Reactions

Grade 8 Science | Rosche

MS-PS1-2 Matter and Its Interactions

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The Phenomenon: The Fading Glow Mystery

Anchoring Context & Focus Question

Why do glow sticks eventually stop glowing?

Methane combustion: one CH4 + two O2 react to form one CO2 + two H2O. Atom counts (1 C, 4 H, 4 O) are equal on both sides — the law of conservation of mass.
Methane combustion at the molecular level — atoms rearrange but mass is conserved.
Diagram of methane combustion showing observable evidence of a chemical reaction — light emission, heat production, and formation of new substances CO2 and H2O
Schematic of methane combustion. Review once before beginning the station activities.
Animated explanation of the week's focus question. Watch then reason about why this happens.
Key Vocabulary (7 terms) — Practice Tool

Cognate Strategy: Many science words look similar in English and Spanish — use your Spanish to learn science!

Term Spanish Definition
chemical reaction reacción química Process where substances transform into new substances
reactant reactivo Starting substance in a chemical reaction
product producto New substance formed in a chemical reaction
conservation of mass conservación de masa Mass is neither created nor destroyed in reactions
precipitate precipitado Solid formed when two solutions are mixed
indicator indicador Substance that changes color to show chemical change
exothermic exotérmico Reaction that releases heat energy

Hook – The Fading Glow Mystery

Observe how glow sticks produce and lose their light over time.
Two beakers, before and after twenty minutes: a shiny nail in clear liquid becomes a pitted, flaking nail in a green, bubbling, warm liquid with orange flakes settling.
The disappearing-nail mystery — every observable change is a clue.

The Disappearing Nail Mystery

A shiny steel nail is dropped into a clear liquid. Twenty minutes later the liquid is green, bubbles are forming, the nail is pitted and coated in orange flakes, and the beaker is warm to the touch. Something has changed — but what, exactly? Is this a chemical reaction, or just mixing?

Cycle 6 Connection

In Cycle 6 you studied forces and Newton's laws — macroscopic changes you could see. This week you'll look at changes at the atomic level: rearrangements of atoms that create entirely new substances. The evidence is still observable — just smaller.

What You'll Do

  1. Watch four short demo videos of real reactions (safely virtualized)
  2. Identify every piece of observable evidence you can
  3. Decide: chemical change, physical change, or unsure? Defend your reasoning
  4. Submit your predictions — you'll revise them after Station 1
COMPLETE THE HOOK FORM

Observe and question what causes glow sticks to fade.

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Worked Example and Simulation – Identifying Evidence of Chemical Reactions

Reference card showing the five observable signs of a chemical reaction: color change, gas production, precipitate formation, temperature change, and light or sound emission.
The five observable evidences — any one is a strong signal.

Worked Example: The Five Evidences of a Chemical Reaction

Problem: How do you tell a chemical change (new substance) from a physical change (same substance, different form)? Chemists use five observable evidences — any ONE is a strong signal a reaction may have occurred.

The Five Evidences

  1. Color change not explained by dilution or mixing
  2. Gas production (bubbles from a non-boiling liquid)
  3. Precipitate (solid forms when two liquids combine)
  4. Temperature change with no external heat source
  5. Light or sound emission (combustion, some redox reactions)

Important Caveat

Evidence ≠ proof. Boiling water looks like it's producing gas, but it's a physical change — same H₂O molecules. To confirm a chemical reaction you need to show that the atoms rearranged into new substances (Station 2 and conservation of mass, MS-PS1-5).

LAUNCH THE REACTION EVIDENCE SIMULATOR

Tip: Use the POE Protocol — Predict what evidence you'll see before running each reaction, Observe the simulator output, then Explain whether mass was conserved.

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Station 1 – Reaction Evidence Lab

Identify signs of chemical reactions through observable evidence.
Two-row classification chart for Station 1's eight demonstrations sorted into chemical changes (top, with new substances formed) and physical changes (bottom, same substance), plus a "needs more info" cell.
Sort each Station 1 demo into chemical, physical, or needs-more-info.

Station 1 — Classifying Reactions by Evidence

Your mission: examine 8 short demonstrations (vinegar + baking soda, dissolving salt, burning paper, rusting iron, mixing two colored solutions that produce a solid, melting ice, copper + silver nitrate, food coloring + water). For each, identify all evidence types present and decide: chemical, physical, or needs more info.

Data Table

For each demo, record: evidence type(s) observed, whether a new substance formed, and whether the change is reversible. Reversibility is a clue but not a definition — some chemical reactions can be reversed under the right conditions.
COMPLETE THE STATION 1 FORM

Observe and classify evidence of chemical reactions.

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Station 2 – Mass Conservation Investigation

Measure mass before and after reactions to test conservation of mass.
A balance scale with a sealed flask of 2 H2 + O2 on the left pan and the same flask after reaction containing 2 H2O on the right pan — both reading 36 grams.
Mass before equals mass after — the closed-system rule.

Station 2 — Atoms Rearrange, Mass Conserves

Reactions don't create or destroy atoms — they rearrange them. In the Worked Example above you ran the simulator and observed this directly. Now apply that understanding: balance the equations below by tracking the mass before and mass after each reaction. The Law of Conservation of Mass (Lavoisier, 1789) is your anchor.

Reactions to Balance

  1. H₂ + O₂ → H₂O (combustion of hydrogen)
  2. CH₄ + O₂ → CO₂ + H₂O (burning methane)
  3. Fe + O₂ → Fe₂O₃ (rusting)
  4. NaHCO₃ + CH₃COOH → CO₂ + H₂O + CH₃COONa (baking soda + vinegar)
COMPLETE THE STATION 2 FORM

Investigate whether mass changes during chemical reactions.

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Station 3 – Design a Reaction Detector

Apply understanding of reaction evidence to design a detection method.
Four illustrated tiles: the Gateway Arch (rust resistance), a person silhouette glowing at the chest (cellular respiration), a frying pan with caramelizing onions, and a glass of fizzing baking-soda-and-lemon-juice.
Reactions you encounter every day in St. Louis.

Station 3 — Chemical Reactions Around You

Your mission: identify the chemical reactions you encounter every day and classify them by evidence type. From cellular respiration in your own body, to the rusting of the Gateway Arch, to the caramelizing of onions on the stove — reactions surround you.

Real-World Reactions to Analyze

  1. Iron + oxygen → rust (slow oxidation) — Gateway Arch stainless-steel choice
  2. Glucose + O₂ → CO₂ + H₂O + ATP (cellular respiration in your cells, right now)
  3. Sugar + heat → caramel (pyrolysis + Maillard reactions)
  4. Baking soda + lemon juice → CO₂ (a neutralization + decomposition reaction)

Argument from Evidence

Write a CER response: "Choose ONE everyday phenomenon. What evidence tells you a chemical reaction is happening, and how do you know new substances formed?"
COMPLETE THE STATION 3 FORM

Design a method to detect whether a chemical reaction has occurred.

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Exit Ticket – Reaction Evidence Integration

Synthesize understanding of chemical reaction evidence and conservation of mass. Spiral questions target MAP Achievement Season standards (PS3.B.1 energy transfer, PS1.A.1 matter structures).
A three-step horizontal synthesis: observe the five evidences → confirm with mass conservation → conclude that a chemical reaction occurred. A connection bar links Cycle 6 forces with Cycle 7 atomic-scale changes.
Synthesizing the week — evidence + conservation = chemical reaction.

Exit Ticket — Reaction Evidence Mastery

Demonstrate your understanding through 2 new-content questions on chemical-reaction evidence, 2 spiral questions from Cycle 6 (forces and motion — what doesn't change at the atomic level during physical change?), and 1 integration question on the SEP practice of analyzing and interpreting data.

COMPLETE THE EXIT TICKET

Demonstrate mastery of chemical reaction evidence concepts.

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Enrichment & Extension
Optional content if you finish early or want to go deeper.

Scientist Spotlight: Dr. Mario J. Molina

Dr. Mario J. Molina (1943–2020) was a Mexican chemist who won the 1995 Nobel Prize in Chemistry for discovering how chlorofluorocarbons (CFCs) — gases used in refrigerators and aerosol cans — destroy the ozone layer. Molina showed that sunlight triggers a chemical reaction: CFCs release chlorine atoms, and each chlorine atom can then break apart 100,000 ozone molecules in a chain reaction. His work led to the 1987 Montreal Protocol, the most successful environmental treaty in history, which phased out CFCs worldwide. The ozone hole is now shrinking. Molina's story shows two things this week's phenomenon makes visible: (1) reactions you can't see with your eyes can transform matter at planet scale, and (2) the evidence of a reaction — a fading glow, a missing mass, a color change — can reveal problems we would otherwise miss until it's too late.

Environmental Justice: Sauget & East St. Louis

Just across the Mississippi from downtown, the village of Sauget, Illinois and parts of East St. Louis hosted chemical plants — Monsanto (later Solutia) and others — that for decades ran industrial-scale chemical reactions producing PCBs, herbicides, and dyes. The reactants went in; the products shipped out; but the byproducts — chemical waste — were dumped into unlined lagoons and the American Bottom floodplain. The surrounding community is roughly 98% Black, and residents show elevated rates of cancer, asthma, and birth defects traced to chemical exposure. Conservation of mass from this week's lesson explains why this matters: the atoms in those byproducts didn't disappear when the plants closed. They stayed in the soil, the groundwater, and the bodies of neighbors. Today, chemists, epidemiologists, and community organizers are using the same detection methods you practice in Station 1 — color-change indicators, precipitate tests, mass balance — to map contamination and demand cleanup.

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Week 1 Complete!

Next Week: Reaction Types & Conservation — how can mixing two clear liquids make a solid appear?